The ND8 works great for some, and others dont like it. Personally id flash ND8 as i get better LTE signal with it. After ND8 boots flash philz recovery in odin 3.07 like he suggested.. go back to recovery and root with the philz option, under the "advanced" menu i believe, and install supersu on the stock rom. Run supersu and it will prompt you to disable knox, just hit yes. Then update to your rom of choice.
Sent from my SPH-L710 using XDA Free mobile app